Guaifenesin, sold under the brand name Mucinex, among others, is a medication used to try to help cough out phlegm from the airways. It is unclear if it decreases coughing. Use is not recommended in children less than 6 years old. It is often used in combination with other medications. It is taken by mouth. Side effects may include dizziness, sleepiness, skin rash, and nausea. While it has not been properly studied in pregnancy, it appears to be safe. It is believed to work by making airway secretions more liquid.